This invention relates to an idling speed feedback control method for internal combustion engines, and more particularly to a method of this kind which is adapted to control the intake air quantity in dependence upon the magnitude of electrical loads on the engine so as to eliminate a lag in the feedback control of the idling speed, at the start of the same control immediately following deceleration of the engine.
A conventional idling speed feedback control method has been known e.g. from Japanese Patent Provisional Publication (Kokai) No. 55-98628, which comprises setting the desired idling speed in dependence upon load on the engine at engine idle, detecting the difference between the desired idling speed and the actual engine speed, and supplying the engine with supplementary air in a quantity corresponding to the detected difference so as to minimize the same difference, to thereby control the engine speed to the desired idling speed.
In the above conventional method, if one or more electrical devices such as head lamps and a radiator cooling fan in a vehicle equipped with the engine are operated at the start of idling speed feedback control (hereinafter merely called "feedback control"), the generator has to function to supply electric power to the electrical devices, causing increased load on the engine and a consequent drop in the engine speed. Such a drop in the engine speed which is caused, particularly at the start of the feedback control immediately following deceleration of the engine, can lead to engine stall upon an increase in the engine load.
In order to overcome such inconvenience, the present assignee has previously proposed an engine speed control method in Japanese Provisional Patent Publication (Kokai) No. 58-197449, which is adapted to detect the on-off state of each one of a plurality of electrical devices, and simultaneously with detection of the on-state of the each device, increase the valve opening period of a control valve for regulating the amount of supplementary air over a predetermined period of time corresponding to the magnitude of electrical load of the each electrical device that is detected to be in the on-state, so as to minimize a lag in control of the supplementary air amount, thereby improving the driveability of the engine.
However, in recent years, various kinds of electrical devices have been installed in a vehicle equipped with an engine so as to improve the driveability of the engine and ensure safety running of the vehicle, which makes it necessary to provide as many sensors and input devices as the electrical devices for detection of the on-off sate of each one of the electrical devices, storing predetermined valve opening values for the supplementary air amount-controlling valve each corresponding to the electrical load of the each electrical device into memory means of the control system, etc., thus making the control program complicated and also increasing the memory capacity of the control system, resulting in disadvantages such as increased manufacturing cost of the control system.